High frequency coil



Jan. 7, 1941.

N. M. RusT HIGH FREQUENCY COIL I Filed April 24, 193s l NvENToR NOEL EYE/a RUST BY g y MH'IL/ ATTORNEY atent'ed 7, 1941v UNITED STATES 'BIGBFREQUENQY con.

.Nol Meyer Bust, Chelmsford, England. asaignor to Radio Corporation of America, a corporation o! Delaware 'Application April zi. 193s, serial No. 76,122

In omi Britain my 11, 193s schim. (ci. 1n-r4.2)

Thisinvention relates to coil constructions for use in electrical high frequency circuits and to circt arrangementsincorporatlng the same.

An important object of the vinvention is to provide improved quarter wave and halt Vwave length `coil constructions which shall be very cheap.v

light, and of low losses and which can be made directly self-supporting. i. e. without needing terminals or mountings. Where terminals or l@ mountings are provided they are arranged to be out ci the field of the coil.

According to this invention a coil structure for use fas a resonant device in high frequency electrical circuit arrangements comprises an inlner conductive cou winding positioned within an outer conductive screen member and is characterized in that said winding and screen member are so constructed and supported that there is no solid dielectric material between the face of said zo winding presented to said screen member and said screen member.

The invention is illustrated in the accompanying drawing in which Fig. lis a longitudinal section of an improved coil construction ci this 25. invention; Fig. 2 is across-section o! Fig. 1; Fig.

3 is an elevation of anothei construction oi' coil structure with part of the screen portion broken sway to show its construction; Fig. 4 is an end view of Fig. 3; Fig. 5 is a developed view of part so of the screen conductor: Fig. 6 is a perspective View of another modiilcation of screen structure to be substituted for the screen structure shown in Figs. 3, ,4 and 5; and Fig. 7 is an end view of Fig. 6. 85 Referring to Figs. 1 and 2 which areI mutually perpendicular sectional views showing one form ci construction in accordance with the invention.

a quarter or' half wave lengthcoil construction comprises a helix l of solid conductive wire or 0. strip e. g. copper, concentrically arranged within a split cylindrical member l of conductlve'material, e. g. ,copper foil.. The helix is wound over parallel insulating support rods l which carry at or near their ends further radial insulating rods '45 l4 which in turn carry additlonalinsulating rods l running parallel to the axis of the helix and also parallel to the rods 3 ,over which the said helixfiswound. The outer insulating rods I serve to support the split toil cylinder I which is- 5o positioned within the said, outer rods I and may be struck or .otherwise amxed thereto .in-.any j convenient manner. vSince in this arrangement the supporting rods 3 -for the helix are inside the turns' thereof and the supporting rods l furthe `ggf'foll are outside the same, the insulating material oi which those rods are constituted will substantially not be cut by the `field between the helix and foil, and accordingly dielectric losses will to a great extent be reduced. It will be appreciated that the middle point of the helix of a half wave 5 coil construction in accordance with the preceding description will be a potential node and ac cordingly it may be directly connected to the split cylinder of foil'.

Referring to Figs. 3 to 5, the' inner conductor of 10 the line is in the form of a helix'- l of ilat strip conductor wound upon and stuck to' an inner L approximately cylindrical former 6 of paper or the like impregnated and coated with a suitable insulating varnish. The former l is somewhat l5 longer Vthan the helix and extends beyond it at both ends. The screen conductor 2 is of copper foil and is stuck to the linside of an approximately cylindrical backing 'l also of paper impregnated with. a suitable varnish. The screen conductor is split with `a plurality of splits l running parallel to the axis of the whole structure, adjacent splits starting from opposite edges and extending rather less than `the length of the screen. The said screen conductor is made by 25 slitting a sheet oi' copper foil as shown in Fig. 5 and then bending it up into a cylinder, the edges, which are at right angles to the slits forming the circular edges of the bent-up cylinder. The conductor 2 with its outer backing 1 is pushed over 30 the inner conductor l and Iformer, and is held in place by strips' i of fairly stift, insulation impregnated or Vcoated paper. The ends of the conductor l are brought out parallel to the axis and are held rmly by insulation coated or impregnated paper layers l0 which pass over the conductor l and also over the strips l and are stuck in position.

. j Figs. 6 and 7 are respectively a perspective view and an end view cfa screen structure which may be substituted for that adopted in the coil structure shown in Figs. 3 tn 5. In Figs. 6 and 7, the screen is in the form of a number of copper foil strips 2a stuck to the inside of an insulation impregnated or coated cylindrical backing 1. 'I'he 45 copper-strips may be earthed as shown in Fig. 6

b y wires lia leading out to a common point. or, instead oi using wires the strips themselves may .be extended beyond the backing and brought out to a common point in the same way as the wires Jlil) .lla ofFig. 6. h

*It 'will be observed that in all the illustrated -coil structures the inner conductor is above its t insulating support. the lace of said conductor presented to the screen being tree ci insulating 5s Y Quarter and haii poses. For example, in the constructions of coil in accordance with this arrangement where there is an outer conductorl or screen having a slit running along'its whole length, means may be provided for increasing and decreasing the width of the slit for tuning purposes; or an auxiliary slotted inner cylinder F (slotted so as' not to act as a short circuiting turn) may be arranged to be slid coaxially to an adjustable extent into the coll proper of the coil construction; or a block or cylinder of ferro-magnetic material may be arranged to bel slid coaxially to an adjustable extent into the said coil proper; or an eddy. Vcurrent conductor mayv be arranged to be slid coaxially to .an adjustable extent into the said coil proper. Another Way of providing for tuning in the case of a half wave length coil construetionis to connect a variable condenser across the ends of the coil proper; or to lconnect a variable condenser between one end of the lcoil proper and the outer conductor; or to connect variable condensers between each end oi the coil proper and the outer conductor. Again tuning may be provided for by so constructing the coil proper that it can be subjected to concertina-like control action, that 'is to. say, so thatits pitch may be varied substantially without altering its diameter or its concentric arrangement within the outer conductor.

What is claimed is:

l. A low loss coil for use as a resonant device in a high frequency circuit comprising an inner conductive coil winding, a cylindrical conductive member located concentric with said conductive coil winding, self-supporting means for said coil winding' including two groups of support mem--v bers oi insulating material located parallel to the axis of said coil, one of said groups located within said coil, the other group located outside of said cylindrical conductive member, radial spacing means interposed between each group of support members and located beyond the ends yof said coil, said cylindrical conductive member positioned between the outside group of insulating members and said coil winding to provide an electrical eld space between said coil and said ylindrical member which is free from solid maerial.

2. A low loss coil for use as a resonant device ina high frequency circuit comprising an inner conductive coil winding, a cylindrical conductive member having a' longitudinal slot locatedvconcentric with said conductive coil Winding, selif supporting means for said coil winding including two groups of support members of insulating material located parallel to the axis of said coll, one of said groups located within said coil, the other group located outside of said cylindrical conductive member, radial spacing means interposed between each group of support members and located'beyond the ends of said coil, said cylindrical conductive member positioned between the outside group of insulating members and said coil winding to provide an electrical ileld space between said coil and said cylindrical member which is free from solid material.

3. A low loss coil for use `as a resonant device in a high frequency circuit comprising an inner conductive coil lwinding, a. cylindrical conductive member having a longitudinal slotlocated concentric with said conductive coil winding, selfsupporting means for said coil winding including two groups of support members oi insulating material located parallel to the axis o! said coil, one of said groups located within said coil, the other group located outside of said cylindrical conductive member, radial spacing meansl located at both ends of said coil and radially with respect to said coil and interposed between said rst and second groups of spacing members to provide an electrical eld space between said coil and said cylindrical member which is free from solid material.

4. A low loss coil for use as a resonant device in a high frequency circuit comprising an inner conductive coil winding, a cylindrical conductive member having a longitudinal slot located con-' centric with said conductive coil winding, selfsupporting means for said coilwinding including two groups of support members of insulating material located parallel tothe axis of said coil, one

of said groups located within said coil, the other thereof.

dii-high frequency wave coil comprising a coil winding, a cylindrical conductive member concentric with said coil winding and having a longitudinakslot therein, a plurality of parallel arranged rods of insulating material positioned along non-adjacent surfaces oi saidcoil and cylindrical ,memben radial spacing means interposed between said parallel arranged rods and c located beyond the endsof said coil and cooperating with said coil, cylindrical member and parallel arranged rods to maintain said coil and said cylindrical member in position, whereby the space between the coil winding and the inside of said conductive member is void of solid lmaterial.

NOEL Merval?u RUST. 

